Download - Food Preservation
university of duhokCollege of veterinary medicine
Food preservation by:mohammad abid
Special thanks to my spervisor: Dr. nechirvan ghafar
Introduction
Food Preservation, processes involved in protecting food against microbes and other spoilage agents to permit its further5 consumption. The preserved food should retain
a palatable appearance, flavor, and texture, as well as its original nutritional value.
The aim of food preservation is to minimize the growth of microorganisms during the storage period, thus
promoting longer shelf life and reduced hazard from eating the food.like,(Animal products).
Food Preservation in History
Nicolas appert(1749-1891)
Principles of preservations
killing of micro-organisms. Inhibition of microbial growth. Removing micro-organisms. Destroying enzyme.
Retardation of chemical changes
Conditions for the growth of micro-organisms
conditions
pH value
oxygen moisture
Microbial Growth
Time and temperature
Methods of the preservation and their side effects
1.Heat treatment2.Irradiation3.Smoking4.Drying and dehydration5.Refrigeration6.Freezing7.Canning8.Sugaring and Salting9.Meat curing10.Pickling in vinegar11.Use of food additives12.Filtration
1.Heat treatment
Principle Food is heated up and cooked. Kills the microorganisms and their spores alters protein structures destroys enzyme activity of microorganisms
Methods of heating1.Blanching2.sterilization3.commercial sterilization4.Pasteurization Levels of pasteurization used to thermally process milk
include:(1) Low Temperature Long Time (LTLT): 63° C (145° F) for 30 min(2) High Temperature Short Time (HTST): 72° C(161° F) for 15 s
(LTLT and HTST are equivalent thermal processes)(3) Ultra High Temperature (UHT): 138° C (280 ° F) (or higher) for
2 s
• Advantage: Inactivates autolysis enzymes. Destroys microorganisms.
• Disadvantage: High temperatures can diminish product
appearance,texture, and nutrient quality.
• Examples: All forms of cooked food, milk sterilized by UHT (ultra high
temperature).
2.Irradiation
Principle Exposing food to ionizing radiation is to destroy enzymes
and micro-organisms in food; kill mould and destroy bacteria in fresh meats.
Irradiated foods are not radioactive Type of radiation used for food preservation is ionizing
radiation.
Advantage: less Nutritional losses The chemical reactions associated with food irradiation do, in
fact, produce very small amounts of new compounds called radiolysis products.
Disadvantage If irradiated food becomes contaminated, new pathogens
have little competition and can multiply more rapidly.
The energy used for irradiated food are: 1.Gamma rays 2.X-rays 3.Electrons (Radura)
3. Smoking Principle The smoke is obtained by burning special type of wood
under low breeze/wind at about 93oC to 104oC. Woods used for smoking are Alder, apple and cherry, hickory,
maple, mesquite, oak, pecan.
Smoking process
Disadvantage smoked foods are carcinogenic.
Examples: Fish (Smoked salmon), ham, and sausage
Smoked ham Smoked sausage
4. Drying and Dehydration
Principle Drying removes the moisture from the food so that bacteria,
yeasts and moulds cannot grow and spoil the food. It also slows down the action of enzymes, but does not inactivate them.
Drying methodsAir
OvenMicrowave oven
Preservation processNormal loss of nutrition Processing method
Canning 60-80% high temperatures
Freezing 40-60% water-logging and rupturing of cells
Dehydrating 5-15% moderate heat and moderate air flow
In-home Drying 3-5% low heat and gentle air flow
DisadvantageDisadvantage Time Time and and workwork, including rehydrating of the food before , including rehydrating of the food before eating.eating.AdvantageAdvantage Drying food loss only a little nutrition Drying food loss only a little nutrition in the food.in the food.
5. Refrigeration Principle process of lowering the temperature and maintaining it in
a given space for the purpose of chilling foods ,Chilling slows down microbial activities and chemical changes resulting in spoilage.
In chilling, food is kept at 0oC - 4oC.
Disadvantage: food cannot be stored for long time.
6. Freezing
Principle It converts water of the food to ice, so the water is
unavailable for metabolic reaction of the microorganisms. In freezing, food temperature is reduced to about -17oC.(Freezer).
Chemical changes during freezing
Enzymes are proteins present in plants and animal. Even after we harvest plants or slaughter animals, enzyme reactions can continue and result in undesirable color, flavor and texture changes in the food. Freezing slows down, but does not destroy enzymes. The two methods you can use are blanching and adding chemical compounds such as ascorbic acid.
Changes in food texture during freezing
• Freezing involves the change of water contained in the food from a liquid to a solid (ice). When water freezes it expands, and the ice crystals formed cause cell walls of food to rupture. As a result, the texture of the product will be much softer when it thaws.
• Disadvantage Freezing would cause low temperature injury.
Examples: Frozen meat, peas, vegetables, ice-cream
7. Canning
Principle Preserving food by heating and sealing in airtight
containers
• Advantage
The steel can recycle process
• Disadvantage
Food are not thoroughly heated or the containers are not properly canned may lead to growth of clostridium botulinum or spoilage of canned food.
Examples: All kinds of tinned foods, such as soup, meat, beans
Canned food
8.Sugaring and Salting
Principle Food is treated with strong salt solution or strong sugar
solution. Disadvantage The food may become very salty or very sweet.• Examples: Bacon, salted fish
9.Meat curing
Principle Meat is treated with salt or strong salt solution containing
NaNO3, KNO3 and which may contain sugar and spices. Salt and sugar both cure meat by osmosis. In addition to
drawing the water from the food, they dehydrate and kill the bacteria that make food spoil.
Nitrite or nitrate are used for retarding rancidity, curing-pink color, killing bacterial
Two curing methods 1. Wet (or brine) curing 2. Dry curing In the wet curing, the curing ingredients were mixed with boiling
water to form”pickling" brine. But in dry curing, the ingredients were simply rubbed into the meat several times over the period of the cure.
• Disadvantage fall in the level of hemoglobin in the blood Malnutrition and reduced lifespan. Nitrates are harmless, but when nitrates are ingested in the diet
they are reduced to nitrites in the body. Then nitrites may react to form nitrosamines.
Nitrosamines are carcinogenic.
• Examples: Salted fish, pork shoulder, ham, corned beef, bacon.
Pork shoulder
10.Pickling in vinegar Principle Food is kept in vinegar since micro-organisms can not
grow well in low pH value solutions. Disadvantage Vinegar is a temporary preservative, because enzymes
continue to act, softening and spoiling the product. Some kind of vinegar such as apple cider vinegar will darken
most vegetables and fruits. Examples: Sauces, pickled onions and cucumbers (no animal
products)
11.Use of food additives
Principle Food Additives, natural and synthetic compounds added to
food to supply nutrients, to enhance color, flavor, or texture, and to prevent or delay spoilage. Some additives can inactivates or kill micro-organisms, retard chemical spoilage.
Types of additives Natural additives
Artificial additives
Functions of food additives Preserve food Do not preserve food • E-number It is the reference number of food additives
The E Number List
• Disadvantage allergic reactions. hyperactivity or asthmatic symptoms especially in children
and young people. certain reactions.
12.Filtration
Principle Filtration can remove microorganisms from the liquid,this
method is used for clearing fluids.